JPH08299971A - Separating injection type ozone contact method - Google Patents

Abstract

PURPOSE: To increase ozone dissolution efficiency and to reduce equipment cost and operation cost. CONSTITUTION: A feed water is branched into two passages, ozone is injected and dissolved only to the feed water 3 flowing in one of the passages, the feed water is joined to the feed water 3 flowing in another passage again and the mixed flow is fed to a residence tank 12. The mixed flow is retained therein for a fixed time and discharged as a treated water. A inexpensive high efficiency water treatment with a simple device is enabled by using a feed water supply pump 19 to inject zone to the suction side and for example, imparting vibration to the pipeline by the addition of a ultrasonic vibration generator to easily obtain the gas-liquid mixed flow of high concn. ozone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separate injection type ozone contact method for water treatment in which ozone is used for sterilization, deodorization, and oxidation of organic substances in water.

[0002]

2. Description of the Related Art In recent years, ozone is diffused in water by utilizing the characteristic that ozone has a strong oxidizing power next to fluorine, so that sterilization, decolorization, deodorization, and removal of organic or inorganic substances by oxidation are performed. Water treatment is widely used. In particular, in the water supply in the suburbs of cities, the damage of offensive odor caused by the water intake source is widespread, and the strong oxidizing power of ozone exerts a great effect in removing this offensive odor. The introduction of advanced processing using is being promoted.

An ozone treatment apparatus for reacting such ozone with organic matter in water treated by ozone (hereinafter referred to as raw water) supplies an ozone generator for generating ozone mainly from electric energy and raw water. It is composed of a water pump, a reaction tank for proceeding the reaction, and an exhaust ozone treatment facility for decomposing the exhaust ozone discharged unreacted from the reaction tank. Generally, the contact method of raw water and ozone is to remove ozone from the lower part of the reaction tank. A bubble column method that blows out as bubbles is used. In recent years, most of them have used a countercurrent contact method in which raw water is supplied from the top of the reaction tank in the bubble column to face ozone gas.In large-scale water purification plants, etc., a crossflow with multiple countercurrent contact ponds connected in series is used. A countercurrent multi-stage contact pond is used.

FIG. 3 is a schematic diagram showing the structure of a cross-flow countercurrent multistage contact basin, including the various devices attached thereto. In FIG. 3, several partition plates 2 are provided in the ozone contact pond 1, and the flow of water is shown by the arrows in FIG. 3, but the raw water 3 is an inlet port at one end of the ozone contact pond 1. 4 flowed in, flowed down in the ozone contact pond 1, moved up between the partition plates 2 and flowed down again, and finally, from the discharge port 5 at the other end of the ozone contact pond 1 as treated water 6 Taken out.

Then, the ozone gas generated by the ozone generator 7 outside the ozone contact pond 1 is introduced from the bottom of the ozone contact pond 1 and brought into contact with the raw water 3 as fine bubbles 9 by the air diffuser 8. Of the ozone injected at this time, unreacted ozone is decomposed by the exhaust ozone treatment facility 10 and released into the atmosphere. These ozone treatment devices require contact time for sufficiently performing an oxidation reaction on raw water. Therefore, when the amount of treated water is large, a large-volume ozone contact pond is required, and when it is introduced into a water purification plant in the suburbs of a city with a large water supply population, large-scale equipment is required. The need for large-scale equipment means
It is not preferable from the economical point of view and becomes a major factor that hinders the introduction of a water treatment apparatus using ozone. Therefore, the ozone treatment apparatus is required to have a high ozone absorption rate and a sufficient organic substance removal efficiency.

[0006] Here, the ozone absorption rate means that of the injected ozone gas, it is dissolved or decomposed in raw water in the reaction tank,
It is the ratio of ozone consumed and is expressed by the following formula.

[0007]

[Equation 1] The removal efficiency is the ratio of water pollutants in the raw water decomposed and removed in the reaction tank, and is represented by the following formula. Typical odorants are water pollutants.

[0008]

[Equation 2] Generally, the higher the ozone absorption rate and the removal efficiency, the better the processing efficiency of the ozone reaction tank.

The amount of ozone transferred when ozone is dissolved in water is the difference between the overall mass transfer capacity coefficient (K _L · a), the saturated ozone concentration in water, and the dissolved ozone concentration (concentration gradient). Is the main factor. This saturated ozone concentration is
It is known to depend on the ozone concentration in the gas and the ozone distribution coefficient. In recent years, from the viewpoint of increasing the ozone dissolution efficiency, the effectiveness of high-concentration ozone has attracted attention,
The examination is progressing in various fields.

However, when water treatment using ozone is carried out in a general water purification plant, the ozone injection amount is set to 1 to 3 mg per liter of raw water. Further, since an ozone generator using air as a raw material is usually used, the generated ozone gas concentration is about 20 mg / L, and the ozone gas flow rate with respect to the raw water flow rate shows a value of 1/20 to 3/20. on the other hand,
Regarding ozone generators, recently, development of high-concentration ozone generators using oxygen as a raw material has progressed, and ozone generation costs have been reduced to the same level as conventional air raw materials. In addition, as described above, since the efficiency of ozone transfer from the gas phase to the liquid phase greatly depends on the concentration of injected ozone gas, it is highly desirable from the viewpoint of mass transfer that the ozone gas concentration be high. .

However, in view of the hydraulic characteristics (gas-liquid flow mode) of the ozone contact pond, it is not preferable that the ozone air flow rate decreases when the injection rate of highly concentrated ozone is constant. In the case of the above-mentioned cross-flow countercurrent multi-stage contact basin, the ozone contact basin originally has the hydraulic characteristic of complete mixing, but when the ozone gas concentration becomes high and the ozone gas flow rate becomes small, mixing due to the rise of bubbles occurs. This is because the stirring effect is reduced and a short-circuit flow and a dead water region are generated. This has been confirmed experimentally by the present inventors that the ozone gas flow rate is 1/100 of the raw water flow rate.
It was found that in the following cases (gas-liquid ratio ≧ 100), poor mixing occurred.

[0012] Therefore, the present inventors found an ozone contact method suitable for high-concentration ozone gas when using a large-scale ozone water purification treatment facility, and found it in Japanese Patent Application No. 7-6795.
Pending. FIG. 4 is a schematic diagram showing a main configuration of a water treatment apparatus to which the separation injection type ozone contact method applied by the present invention is applied, and portions common to FIG. 3 are represented by the same reference numerals. Hereinafter, with reference to FIG. 4, a water purification process using ozone will be described together with the configuration of this apparatus.

In FIG. 4, this apparatus has an ozone dissolution section 11 and a retention section 12 surrounded by a dotted line in the system,
The pipe flow path is branched into these two parts to allow the raw water 3 to flow. First, the raw water 3 flows into the system from the introduction port 13, is branched to the ozone dissolving portion 11 side at a branch point 14 using a valve, for example, reaches the ozone dissolving device 15, and the ozone gas sent from the ozone generating device 7 is injected therein. Mixed and mixed. As the ozone dissolving device 15, an ordinary bubble column or a mixing device such as an ejector is used. The amount of branched water to the ozone dissolving part 11 side can be arbitrarily determined in consideration of the water quality of the raw water 3 and the treatment scale of the entire equipment, but the amount of branching water to the ozone dissolving part 11 side should be reduced. If possible, the ozone dissolving device 15
This reduces the load on the equipment and contributes to a reduction in equipment costs.

Next, the raw water 3 discharged from the ozone dissolving device 15
(Ozone-mixed raw water) enters from the inlet 13 and branches off 1
In 4 the raw water 3 which goes straight in the pipe without advancing to the ozone dissolving part 11 side is mixed and mixed at the confluence point 16 and reaches the mixing device 17 such as a baffle plate or a line mixer to secure the mixing property. The device 17 is not always necessary depending on the situation. Then, merging mixed raw water 3 is flows into the retention portion 12, retaining portion 12 is made of retention vessel having almost the same structure as the ozone contact basin 1 shown in FIG. 3, a plurality in the tank The partition plate 2 is installed to provide a vertical bypass structure, so that the flow of water in the retention section 12 is made uniform and the occurrence of a short-circuit flow is suppressed.

In this way, the raw water 3 mixed with ozone can be sent out of the system as treated water 6 from the discharge port 18 after staying for a certain time in the staying section 12 . The exhaust ozone treatment facility 10 is the same as that described above. Retention area
The retention time of 12 (retention tank) is required to allow the decomposition reaction of organic substances to proceed, and is set to about 10 to 20 minutes when removing odorous substances, for example. Therefore, although the volume of the retention section 12 increases according to the amount of treated water, unlike the case of the cross-flow countercurrent multistage contact basin shown in FIG. Yes, the manufacturing cost is low, and the gas-liquid ratio is always kept high without causing a poor mixing of the raw water 3 and ozone, and a high removal rate of organic substances can be obtained.

[0016]

As described above, the separation injection type ozone contact method is a method suitable for high-concentration ozone gas in a large-scale water purification treatment facility using ozone. Subsequent research at the Institute revealed that there is still room for improvement. This is because the ozone dissolving device used for the separation injection type ozone contacting method is required to have a higher ozone dissolving efficiency, and at the same time, it can reduce the equipment cost and the operating cost as compared with the conventional cross flow type ozone contacting pond. It is necessary.

Comparing various ozone contacting methods,
The bubble column type requires less ozone injection power, but requires a certain amount of contact time and the water depth of the reaction column to obtain sufficient dissolution efficiency, resulting in high equipment costs and advantages in terms of installation area and height. In addition, the method using a pressure pump or an ejector can keep the equipment cost of the reaction tower and the like low, but since it is necessary to give a certain flow velocity and pressure to the raw water, the power cost for ordinary operation is low. Therefore, it is not suitable for large-scale processing equipment.

Therefore, in order to apply it to various ozone treatment equipments and reduce equipment cost and operation cost, there are great expectations for the separation injection type ozone contacting method. The present invention has been made in view of the above points, and an object thereof is to use a raw water supply pump in a separation injection type ozone contact method to increase ozone dissolution efficiency and reduce equipment cost and operation cost. To provide.

[0019]

In order to solve the above-mentioned problems, the present invention is a partial modification of the separation injection type ozone contact method which the present inventors applied for in Japanese Patent Application No. 7-6795. That is, the raw water is branched into two flow paths, and ozone is injected into one flow path in which the ozone dissolving section for flowing the raw water is formed by using the raw water supply pump to dissolve the raw water, and the water is flowed through the other flow path. The raw water is re-merged and mixed, and this mixed flow is sent to a retention part consisting of a tank having a plurality of partition plates, where it is retained as an upper and lower bypass flow for a certain period of time, and then a series of steps for extracting the treated water is performed. At this time, ozone is injected into the suction side of the raw water supply pump, and an ultrasonic oscillator is added to the pipe between the discharge side of the raw water supply pump and the raw water confluence to prevent ozone gas bubbles from assembling. It suppresses.

[0020]

As described above, in the present invention, the raw water supply pump is used in the ozone dissolving section, and the ozone gas is injected from the suction side of the raw water supply pump. The high-concentration ozone has a high dissolution rate in the raw water and the injection air volume is also high. The gas-liquid ratio becomes large because it decreases, and it is easy to obtain a gas-liquid mixed flow. While the injected ozone gas flows in the pipe as a gas-liquid mixed flow, ozone is dissolved (transition from gas phase to liquid phase). Is completed.

[0021]

EXAMPLES The method of the present invention will be described below based on examples. FIG. 1 is a schematic diagram showing a configuration of a main part of a water treatment apparatus to which a separation injection type ozone contacting method according to the present invention is applied, and the same portions as those in FIG. 4 are denoted by the same reference numerals. The configuration of the apparatus shown in FIG. 1 is basically the same as that shown in FIG. 4, and the only difference is that the ozone dissolving apparatus 15 is replaced with a raw water supply pump 19. Therefore, only the essential points of the present invention will be described here.

Raw water 3 flows into the system through the inlet 13, and flows at the branch point 14 to the ozone dissolving section 11 side and the retention section.
It branches into the flow path to the 12 side. Of the branched raw water 3,
The flow on the side of the retention unit 12 is determined by the natural flow rate from a treatment process (for example, a coagulation sedimentation tank) in the preceding stage (not shown), while the flow on the side of the ozone dissolution unit 11 is maintained by the raw water supply pump 19. .

The ozone gas generated from the ozone generator 7 is supplied to the raw water 3 from the ozone injection point 20 on the suction side of the raw water supply pump 19. Normally, the ozone gas generated from the ozone generator 7 has a discharge pressure of about 1.6 Kg / cm ² , and the suction side of the raw water supply pump 19 has a slight negative pressure. The injection is done without going against the flow. Raw water supply pump 1
When ozone gas is supplied to the suction side of 9, the pump flow rate and discharge pressure decrease, but the flow on the ozone dissolving section 11 side can be stabilized by increasing the ozone gas concentration to be used and reducing the ozone gas flow rate. Further, by reducing the flow rate of ozone gas, the ozone gas becomes the raw water 3 and a gas-liquid mixed flow, flows through the raw water supply pump 19 and the pipe, and the ozone is dissolved, that is, the transition from the gas phase to the liquid phase proceeds.

After that, the same process as described with reference to FIG. 4 is followed, and the raw water 3 flowing on the ozone dissolving section 11 side merges at the confluence point 1.
In step 6, the raw water 3 on the side of the retention section 12 is mixed again, and after being retained in the retention tank of the retention section 12 for a certain period of time, the unreacted exhaust ozone is discharged to the outside of the system by the exhaust ozone treatment facility 10. Be disassembled. As described above, according to the method of the present invention, ozone is originally dissolved in water faster than air, and is dissolved in the outlet side of the raw water supply pump 19 together with the effect that the dissolution rate is further increased due to the high concentration of ozone. Sufficient dissolution efficiency can be obtained without providing a tank or the like. In addition, the raw water supply pump 19 used here does not require the power required by the conventional pressurizing pump or ejector pump, and has a natural flow velocity, so that both the equipment cost and the operating cost can be reduced.

By the way, as described above, the ozone dissolving apparatus used in the separate injection type ozone contact pond is required to have a high ozone dissolving efficiency. To improve the ozone dissolving efficiency, the general mass transfer described above is required. capacity coefficient (K _L · a)
Is important. Among these, a represents the gas-liquid contact area (per unit cross-sectional area) of ozone gas mixed as bubbles in raw water. When the flow rate of injected ozone gas is constant, the value of a becomes larger as each bubble of the ozone gas is smaller, that is, the number of bubbles of ozone gas is larger, resulting in improvement of ozone dissolution efficiency. To do.

In the ozone injection method for the separate injection type ozone contact pond shown in FIG. 1, since ozone gas is injected into the suction side of the raw water supply pump 19 as an ozone dissolving device, the injected ozone gas bubbles are strongly discharged in the pump. By shearing and mixing, the bubbles become smaller and the value of a temporarily rises, but after that, the bubbles are discharged from the pump and the discharge side as a gas-liquid mixed flow, and while flowing in the pipe, the bubbles are In the center of the inside, they are aggregated and associated, and the final bubble diameter becomes large. This is due to the flow velocity distribution inside the pipe, and it is considered that the flow velocity in the central portion of the pipe is higher than that in the wall portion of the pipe, so that the bubbles are attracted to the central portion of the pipe and aggregate.

When the bubble diameter becomes large, the value of a becomes small, and as a result, the ozone dissolution efficiency of the contact pond decreases. Therefore, in order to keep the ozone transfer efficiency in the separate injection type ozone contact pond high, a method for preventing bubbles from associating and coalescing in the pipe is required. FIG. 2 is a schematic diagram showing a configuration of a main part of a water treatment device made in consideration of the above points, and portions common to FIG. 1 are denoted by the same reference numerals.

The configuration of the apparatus shown in FIG. 2 is basically the same as that shown in FIG. 1, but the difference in the ozone contacting method is in the vicinity of the ozone dissolving section 11 in the raw water supply pump 1.
Using an ultrasonic oscillator 21 installed between the discharge side of 9 and the confluence 16 to a gas-liquid mixed flow containing ozone gas bubbles,
It means that the ultrasonic vibration is always applied. As the vibrator of the ultrasonic oscillator 21 used here, a relatively inexpensive barium titanate-based magnetic vibrator or the like is used, and the shape thereof is also cylindrical, so that uniform vibration can be given to the inside of the pipe. it can. By doing so, it is possible to prevent the bubbles from being dispersed and associated with each other, and it is possible to efficiently proceed the transfer of ozone from the gas phase to the liquid phase.

As a secondary effect, when ultrasonic waves are applied to a liquid, bubbles are generated and crushed to locally raise the temperature to cause a chemical reaction to generate hydrogen peroxide (H ₂ O ₂ ). It is said that the addition of hydrogen peroxide in the reaction of ozone and pollutants may accelerate the oxidative decomposition reaction, so it is expected that the reactivity will be improved as compared with ordinary ozone treatment alone. it can.

[0030]

EFFECTS OF THE INVENTION In recent years, the performance of ozone generators has improved, and high concentration ozone has come to be used for water treatment. When high concentration ozone is used, a cross flow countercurrent multi-stage contact pond is used for raw water. Since it is not preferable to use the conventional method as it is because the mixing state of ozone and ozone is bad and the equipment cost of the down dissolution type water treatment equipment is high, a new ozone injection method compatible with high concentration ozone is recommended. Had to develop.

On the other hand, the present inventors have applied for a separate injection type ozone contacting method according to Japanese Patent Application No. 7-6795. In the present invention, a part of the method is improved to supply raw water as an ozone dissolving device. A pump is provided to inject ozone gas from the suction side of the raw water supply pump, and vibration is applied by an ultrasonic oscillation device added between the ozone dissolution part and the confluence of the two flow paths to allow ozone gas bubbles to associate with each other. The high dissolution rate of high-concentration ozone, such as the suppression of ozone, is utilized, and the equipment is simplified and the power of the pump is reduced as well as the sufficient dissolution efficiency. It is expected to be adopted as an extremely effective ozone contact method not only when expanding the range of application to various water treatment equipment used but also when newly introducing water treatment equipment using ozone. That.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main configuration of a water treatment device to which the method of the present invention is applied.

FIG. 2 is a schematic diagram showing a configuration of a main part of a water treatment device to which the method of the present invention, to which an ultrasonic oscillator is added, is applied in FIG.

FIG. 3 is a schematic diagram showing a main configuration of a water treatment device using a cross-flow countercurrent multistage contact basin.

FIG. 4 is a schematic diagram showing a configuration of a main part of a water treatment apparatus to which a separation injection type ozone contact method applied by the present inventors is applied.

[Explanation of symbols]

1 Ozone Contact Pond 2 Partition Plate 3 Raw Water 4 Inlet 5 Outlet 6 Treated Water 7 Ozone Generator 8 Diffuser 9 Bubble 10 Waste Ozone Treatment Facility 11 Ozone Dissolving Part 12 Retention 13 Inlet 14 Branch Point 15 Ozone Dissolving Device 16 Confluence point 17 Mixing device 18 Discharge port 19 Raw water supply pump 20 Ozone injection point 21 Ultrasonic oscillator

Claims (2)

[Claims] 1. Raw water introduced into a pipe system is branched into two flow passages, and ozone is injected into one flow passage formed with an ozone dissolving portion for flowing the raw water using a raw water supply pump to dissolve the raw water. Is mixed again with the raw water flowing through the other flow path,
This mixed flow is sent to a retention part consisting of a tank having a plurality of partition plates, and after it is retained as an upper and lower bypass flow for a certain period of time, a separated injection type ozone contact method for extracting treated water is performed. A separate injection type ozone contact method characterized by injecting ozone into the suction side. 2. When carrying out the method according to claim 1, bubbles of ozone gas are generated by using an ultrasonic oscillator installed in a pipe between the discharge side of the raw water supply pump and the confluence of the raw water in the vicinity of the ozone dissolving section. A separate injection type ozone contact method characterized by suppressing association.